Pulse measurement device, pulse measurement method, and pulse measurement program

ABSTRACT

A pulse wave signal expressing a pulse is obtained by detecting a pulse of a measurement subject using a pulse wave sensor. The pulse wave signal is stored in a storage unit. A frequency spectrum of the pulse wave signal is found by converting the time-domain pulse wave signal stored in the storage unit into the frequency domain. It is determined whether or not the measurement subject is at rest by finding a frequency range, within a predetermined total frequency range the pulse rate of a person can take on, in which an intensity of a frequency component of the frequency spectrum exceeds a first threshold, and finding whether or not a ratio of the frequency range with respect to the total frequency range is less than a second threshold. A pulse rate from the point in time when the measurement subject has been determined to be at rest is found as the measurement subject&#39;s at-rest pulse rate.

This application is a continuation application of U.S. patentapplication Ser. No. 14/629,010 filed Feb. 23, 2015, which is in turn aU.S. National Stage of International Application No. PCT/JP2013/071814filed Aug. 12, 2013, which claims the benefit of Japanese PatentApplication No. 2012-201912 filed Sep. 13, 2012. The disclosure of theprior applications is hereby incorporated by reference herein in theirentirety.

TECHNICAL FIELD

This invention relates to pulse measurement devices and pulsemeasurement methods, and particularly relates to pulse measurementdevices and pulse measurement methods capable of correctly measuring ameasurement subject's pulse rate.

This invention also relates to pulse measurement programs that cause acomputer to execute such a pulse measurement method.

BACKGROUND ART

A device that measures a measurement subject's pulse rate (heart rate)by wrapping a belt to which an electrocardiographic sensor is attachedaround the measurement subject's chest area and measuring the beating ofthe measurement subject's heart electrocardiographically can be given asa conventional example of this type of device.

There is also a device that measures a pulse rate by detecting pulsatorymotion in a measurement subject's blood vessel in anon-electrocardiographic manner, unlike the aforementioned device thatelectrocardiographically detects a measurement subject's heartbeat.

A device that measures a measurement subject's pulse rate byphotoelectrically detecting pulsatory motion in a measurement subject'ssubcutaneous blood vessel using a photoelectric sensor can be given asan example of the latter type of device (see Patent Literature 1 (JPH10-234684A), for example).

In the latter type of device, a signal expressing pulsatory motion inthe measurement subject's subcutaneous blood vessel (a pulse wavesignal) is obtained and the pulse rate is measured based on the cyclicnature of fluctuations in the pulse wave signal over time.

CITATION LIST Patent Literature

Patent Literature 1: JP H10-234684A

SUMMARY OF INVENTION Technical Problem

However, with a device that employs a method in which the measurementsubject's pulse rate is measured by detecting pulsatory motion in themeasurement subject's subcutaneous blood vesselnon-electrocardiographically, such as photoelectrically, it is difficultto correctly measure the measurement subject's pulse rate when themeasurement subject is exercising, for example.

The reason for this is that if the measurement subject is exercisingduring the measurement, the blood vessel experiences acceleration due tothe exercise, and irregularities arise in the blood flow as a result.These irregularities are superimposed on the pulse wave signal asexternal disturbance components. This makes it difficult to extract thecycle of the temporal fluctuations caused by the pulsatory motion fromthe pulse wave signal.

Meanwhile, when the measurement subject is exercising, a sensor meansattached to a part of the measurement subject's body will alsoexperience acceleration, which results in a phenomenon in which thesensor means shifts position relative to that part of the body,separates from the part of the body even temporarily, and so on. Thisphenomenon also appears as an external disturbance componentsuperimposed on the pulse wave signal. Such a phenomenon is anothercause of difficulty in extracting the cycle of the temporal fluctuationcaused by the pulsatory motion from the pulse wave signal.

Accordingly, in the case where a method for measuring a measurementsubject's pulse rate by detecting pulsatory motion in the measurementsubject's subcutaneous blood vessel non-electrocardiographically, suchas photoelectrically, is employed, it has been desirable to first obtainthe pulse rate while the measurement subject is at rest, and then trackand find the measurement subject's pulse rate during exercise using theat-rest pulse rate as a reference.

Accordingly, it is an advantage of this invention to provide a pulsemeasurement device and a pulse measurement method capable of determiningwhether or not a measurement subject is at rest and correctly measuringthe measurement subject's pulse rate while at rest.

It is a further advantage of this invention to provide a pulsemeasurement program capable of causing a computer to execute such apulse measurement method.

Solution to Problem

To achieve the aforementioned advantage, a pulse measurement deviceaccording to this invention includes a data obtainment unit configuredto obtain a pulse wave signal expressing a pulse by detecting a pulse ofa measurement subject using a pulse wave sensor, a storage unitconfigured to store the pulse wave signal, a frequency conversion unitconfigured to find a frequency spectrum of the pulse wave signal byconverting the time-domain pulse wave signal stored in the storage unitinto a frequency domain, a rest state determination unit configured todetermine whether or not the measurement subject is at rest by finding afrequency range, within a predetermined total frequency range the pulserate of a person can take on, in which an intensity of a frequencycomponent of the frequency spectrum exceeds a first threshold, andfinding whether or not a ratio of the said frequency range with respectto the total frequency range is less than a second threshold, and apulse rate obtainment unit configured to find a pulse rate from thepoint in time when the measurement subject has been determined to be atrest as the measurement subject's at-rest pulse rate.

Note that in the present specification, the data obtainment unit mayobtain the pulse wave signal directly from the pulse wave sensor, or mayinstead temporarily store the pulse wave signal from the pulse wavesensor in a server (having a storage unit) or the like and then obtain(indirectly obtain) the signal from the server or the like.

Furthermore, a “person” and the “measurement subject” may be the sameperson. The “person” may be multiple people, and may include the“measurement subject” in such a case.

Meanwhile, in the case where there are a plurality of frequency rangesin which the intensity of the frequency component of the frequencyspectrum exceeds the first threshold are present in the total frequencyrange, it is assumed that those frequency ranges are totaled and theratio of those frequency ranges with respect to the total frequencyrange is calculated.

Here, “pulse rate” refers to a number of pulses per unit of time (forexample, beats per minute (BPM), which is the number of pulses perminute). The pulse rate at a given “point in time” refers to the pulserate that takes that point in time as an end point of a measurementperiod.

In the pulse measurement device according to this invention, the dataobtainment unit obtains a pulse wave signal expressing a pulse bydetecting the pulse of a measurement subject using a pulse wave sensor.The storage unit stores the pulse wave signal. The frequency conversionunit finds a frequency spectrum of the pulse wave signal by convertingthe time-domain pulse wave signal stored in the storage unit into afrequency domain. The rest state determination unit determines whetheror not the measurement subject is at rest by finding a frequency range,within a predetermined total frequency range the pulse rate of a personcan take on, in which an intensity of a frequency component of thefrequency spectrum exceeds a first threshold, and finding whether or nota ratio of the said frequency range with respect to the total frequencyrange is less than a second threshold.

Here, finding a frequency range in which the intensity of the frequencycomponent of the frequency spectrum exceeds the first threshold withinthe predetermined total frequency range a person's pulse rate can takeon refers to focusing only on the main intensity peaks contained withinthe frequency spectrum and eliminating small intensity components (forexample, frequency components produced by comparatively light exerciseperformed by the measurement subject, harmonic components, and so on).Meanwhile, in the case where the ratio of those frequency ranges (thefrequency ranges in which the intensity of the frequency component ofthe frequency spectrum exceeds the first threshold) with respect to thetotal frequency range is less than the second threshold, it is thoughtthat only a basic intensity peak for when the measurement subject is atrest is present in the total frequency range, and that other intensitypeaks (different from the basic intensity peak) produced when themeasurement subject exercises comparatively vigorously are not present.Accordingly, the rest state determination unit can correctly determinewhether or not the measurement subject is at rest.

Then, the pulse rate obtainment unit finds a pulse rate from the pointin time when the measurement subject has been determined to be at restas the measurement subject's at-rest pulse rate. Accordingly, accordingto the pulse measurement device, the measurement subject's at-rest pulserate can be measured correctly. As a result, the measurement subject'spulse rate during exercise is tracked and found, using the at-rest pulserate as a reference.

In the pulse measurement device according to an embodiment, the pulsewave sensor is a photoelectric sensor including a light-emitting unitconfigured to emit light toward the measurement area at a given emittedlight intensity and a light-receiving unit that receives light reflectedby or transmitted through the measurement area.

With the pulse measurement device according to this embodiment, thephotoelectric sensor is provided as a pulse wave sensor, and thus thepulse wave information, including the pulse, can be detected accuratelywith a simple configuration.

In the pulse measurement device according to an embodiment, the pulserate obtainment unit finds, as the measurement subject's at-rest pulserate, a frequency indicating a maximum intensity peak among theintensity peaks contained in the frequency spectrum when it has beendetermined that the measurement subject is at rest.

With the pulse measurement device according to this embodiment, usingthe result of the frequency conversion performed by the frequencyconversion unit, the measurement subject's at-rest pulse rate can befound with ease.

In the pulse measurement device according to an embodiment, the firstthreshold is set to a certain ratio with respect to the intensity of themaximum intensity peak among the intensity peaks contained in thefrequency spectrum.

With the pulse measurement device according to this embodiment, thefirst threshold is set to a certain ratio with resepct to the intensityof the maximum intensity peak among the intensity peaks contained in thefrequency spectrum. In other words, as a result of the frequencyconversion performed by the frequency conversion unit, when theintensity (raw data) of the maximum intensity peak contained in thefrequency spectrum has changed, the first threshold is set asappropriate in a variable manner so as to eliminate small intensitycomponents in accordance with the change (that is, noise such asfrequency components produced due to the measurement subject performingcomparatively light exercise).

In the pulse measurement device according to an embodiment, thefrequency conversion unit segments the time-domain pulse wave signalstored in the storage unit into periods of a predetermined given lengthand finds a frequency spectrum of the pulse wave signal by convertingthe pulse wave signal into the frequency domain cyclically; and the reststate determination unit determines whether or not the ratio is lessthan the second threshold for the frequency spectra of the pulse wavesignal found cyclically, and determines that the measurement subject isat rest when the ratio is less than the second threshold a plurality oftimes in succession.

In the pulse measurement device according to this embodiment, thefrequency conversion unit segments the time-domain pulse wave signalstored in the storage unit into periods of a predetermined given lengthand finds a frequency spectrum of the pulse wave signal by convertingthe pulse wave signal into the frequency domain cyclically. The reststate determination unit determines whether or not the ratio is lessthan the second threshold for the frequency spectra of the pulse wavesignal found cyclically, and determines that the measurement subject isat rest when the ratio is less than the second threshold a plurality oftimes in succession. Accordingly, whether or not the measurement subjectis at rest can be determined even more correctly.

A pulse measurement method according to this invention includes a stepof obtaining a pulse wave signal expressing a pulse by detecting a pulseof a measurement subject using a pulse wave sensor and storing the pulsewave signal in a storage unit, a step of finding a frequency spectrum ofthe pulse wave signal by converting the time-domain pulse wave signalstored in the storage unit into a frequency domain, a step ofdetermining whether or not the measurement subject is at rest by findinga frequency range, within a predetermined total frequency range thepulse rate of a person can take on, in which an intensity of a frequencycomponent of the frequency spectrum exceeds a first threshold, andfinding whether or not a ratio of the said frequency range with respectto the total frequency range is less than a second threshold, and a stepof finding, as the measurement subject's at-rest pulse rate, a frequencyindicating a maximum intensity peak among the intensity peaks containedin the frequency spectrum when it has been determined that themeasurement subject is at rest.

According to the pulse measurement method of this invention, themeasurement subject's at-rest pulse rate can be measured correctly. As aresult, the measurement subject's pulse rate during exercise is trackedand found, using the at-rest pulse rate as a reference.

A pulse measurement program according to this invention is a program forcausing a computer to execute the aforementioned pulse measurementmethod.

According to the pulse measurement program of the invention, a computercan be caused to execute the aforementioned pulse measurement method.

Advantageous Effects of Invention

As is clear from the foregoing, according to the pulse measurementdevice and the pulse measurement method of this invention, whether ornot a measurement subject is at rest can be determined and themeasurement subject's pulse rate while at rest can be measuredcorrectly.

Meanwhile, according to the pulse measurement program of the invention,a computer can be caused to execute the aforementioned pulse measurementmethod.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a cross-sectional view schematically illustrating a pulsemeasurement device according to an embodiment of this invention.

FIG. 2 is a block diagram illustrating the functional configuration ofthe pulse measurement device.

FIG. 3 is a diagram illustrating an example of the circuit configurationof a measurement unit for measuring a pulse wave signal in the pulsemeasurement device.

FIG. 4 is a diagram illustrating an example of a pulse wave signalwaveform.

FIG. 5 is a diagram illustrating an example of the waveform of an ACcomponent in a pulse wave signal.

FIG. 6 is a diagram illustrating a method for determining whether or nota measurement subject is at rest.

FIG. 7 is a diagram illustrating an example of a frequency spectrum of apulse wave signal while at rest.

FIG. 8 is a diagram illustrating an example of a frequency spectrum of apulse wave signal during exercise.

FIG. 9 is a diagram illustrating a flow of operations performed by thepulse measurement device.

FIG. 10 is a diagram illustrating an example of a frequency conversiontiming.

FIG. 11 is a diagram illustrating another example of a frequencyconversion timing.

DESCRIPTION OF EMBODIMENTS

Hereinafter, an embodiment of the invention will be described in detailwith reference to the drawings.

FIG. 1 schematically illustrates the configuration of a pulsemeasurement device according to an embodiment. Note that for descriptivepurposes, a side of a main body 10 located toward a measurement area(not shown) will be referred to as a “bottom surface side”, whereas aside of the main body 10 on the side opposite from the measurement areawill be referred to as a “top surface side”.

A pulse measurement device 1 includes the main body 10 and a band 20.

The main body 10 of the pulse measurement device 1 has a layeredstructure in which a base portion 11, a neck portion 12, and a topportion 13 are layered in sequence from a bottom surface 15 to a topsurface 16. The neck portion 12 is located between the base portion 11and the top portion 13. The main body 10 includes the bottom surface 15that is disposed in tight contact with the measurement area (not shown)of the measurement subject and forms a surface of contact with themeasurement area, and the top surface 16 located on the side oppositefrom the bottom surface 15. The main body 10 has a stepped structure inwhich the size of the top portion 13 is configured to be smaller thanthe size of the base portion 11 and the size of the neck portion 12 isconfigured to be smaller than the size of the top portion 13, in aplanar direction that follows the bottom surface 15. In other words, theneck portion 12 of the main body 10 has a recessed shape.

The main body 10 of the pulse measurement device 1 includes ameasurement unit 50 that is disposed on the bottom surface 15 side andis configured of a pulse wave sensor that measures the measurementsubject's pulse, and a display unit 114 that is disposed on the topsurface 16 side and displays information regarding the pulse measured bythe measurement unit 50. The measurement unit 50 disposed on the bottomsurface 15 side is an optical sensor that includes a light-emittingelement 54, such as a light-emitting diode, that emits infrared light ornear-infrared light, and a light-receiving element 56 such as aphotodiode or a phototransistor. The light-emitting element 54 functionsas a light-emitting unit that irradiates the measurement area with lighthaving a given emitted light intensity. Meanwhile, the light-receivingelement 56 functions as a light-receiving unit that receives reflectedlight or transmitted light from the measurement area.

When the main body 10 is disposed in tight contact with the measurementarea and an artery in the measurement area is irradiated withmeasurement light (infrared light or near-infrared light, for example)emitted from the light-emitting element 54, the irradiated light isreflected by red blood cells flowing in the artery and the reflectedlight is received by the light-receiving element 56. The amount ofreflected light received by the light-receiving element 56 changesdepending on pulsatory motion in the artery. Accordingly, pulse waveinformation can be detected and the pulse rate can be measured by themeasurement unit 50. Although the measurement unit 50 is disposed so asto make contact with the bottom surface 15 in FIG. 1, it should be notedthat the configuration may be such that the measurement unit 50 isdisposed within the main body 10 and a spatial portion that communicatesbetween the measurement unit 50 disposed within the main body 10 and thebottom surface 15 of the main body 10 is provided. Furthermore, althoughthe pulse measurement device 1 illustrated in FIG. 1 is a type in whichthe measurement unit 50 is configured of the light-emitting element 54and the light-receiving element 56 disposed in the vicinity of thelight-emitting element 54 and detects light reflected by the measurementarea, the device may be a type in which the measurement unit 50 isconfigured of the light-emitting element 54 and the light-receivingelement 56 disposed facing the light-emitting element 54 and detectstransmitted light that has passed through the measurement area.

The pulse measurement device 1 includes the measurement unit 50,configured of a photoelectric sensor, as a pulse wave sensor, and thusthe pulse wave information, including the pulse, can be detectedaccurately with a simple configuration.

The display unit 114 is disposed on the top surface 16 side, or in otherwords, in the top portion 13, of the main body 10. The display unit 114includes a display screen (for example, a liquid-crystal display (LCD)or an electroluminescence (EL) display). The display unit 114 displaysinformation regarding the measurement subject's pulse (the pulse rate,for example) and so on in the display screen. Control of the displayscreen is carried out by a control unit 111 (mentioned later)functioning as a display control unit.

The band 20 for affixing the main body 10 to the measurement area of themeasurement subject includes a main body holding portion 23 for holdingthe main body 10 in tight contact and a wrapping portion 25 for wrappingaround the measurement area.

A size of an opening 24 formed in the main body holding portion 23 isconfigured to approximately match the outer size of the recessed neckportion 12. Through this, an outer portion of the neck portion 12 andthe approximately rectangular opening 24 engage.

A buckle member 30 that is bent into an approximately rectangular shapeis attached to a left side end portion 29 of the main body holdingportion 23. An end portion 27 of the wrapping portion 25 is passedthrough a hole 32 in the buckle member 30 so as to face outward from themeasurement area, and is then folded back.

A relatively long female-side surface fastener 26 that extends in alonger direction is provided on an outer circumferential surface 22 a (asurface opposite from an inner circumferential surface 22 b that makescontact with the measurement area) in an area of the wrapping portion 25aside from the end portion 27. A relative short male-side surfacefastener 28 that extends in the longer direction is attached to an areaof the end portion 27 that has been folded over and is on the rear sideas a result. The female-side surface fastener 26 and the male-sidesurface fastener 28 are engaged with each other so as to be freelydetachable from each other.

The main body 10 is held in tight contact with the measurement area bythe band 20 in this manner.

FIG. 2 illustrates a functional block configuration of the pulsemeasurement device 1. The main body 10 of the pulse measurement device 1includes the control unit 111, a storage unit 112, a power source 113,the display unit 114, an operating unit 115, the measurement unit 50,and a communication unit 122.

The control unit 111 includes a central processing unit (CPU) as well asauxiliary circuitry thereof, controls the various units that configurethe pulse measurement device 1, and executes various types of processesin accordance with programs and data stored in the storage unit 112. Inother words, the control unit 111 processes data inputted through theoperating unit 115 and the communication unit 122, and stores theprocessed data in the storage unit 112, displays the processed data inthe display unit 114, outputs the processed data from the communicationunit 122, or the like.

The storage unit 112 includes a RAM (random access memory) used as awork region required by the control unit 111 to execute programs, and aROM (read-only memory) for storing basic programs to be executed by thecontrol unit 111. A semiconductor memory (a memory card, a solid-statedrive (SSD)) or the like may be used as a storage medium in an auxiliarystorage unit for complementing a storage region in the storage unit 112.The storage unit 112 can store, in time series, a pulse signal (and anAC component thereof in particular) expressing the measurement subject'spulse as detected by the measurement unit 50, on a measurementsubject-by-measurement subject basis.

The operating unit 115 includes, for example, a power switch manipulatedto turn the power source 113 of the pulse measurement device 1 on oroff, and an operating switch manipulated to select the measurementsubject for whom a measurement result obtained on a measurementsubject-by-measurement subject basis is to be saved in the storage unit112 or to select the type of measurement to be carried out. Note thatthe operating unit 115 can be provided on the top surface 16 of the mainbody 10 or a side surface.

The communication unit 122 is used in order to send data generated bythe control unit 111, data stored in the storage unit 112, and so on toa server over a wired or wireless network, to receive data generated bya control unit (not shown) of the server, data stored in a storage unit(not shown) of the server, and so on, and the like. Here, “server” is abroad concept that includes, for example, a stationary terminal such asa personal computer, a mobile terminal such as a cellular phone, asmartphone, a PDA (personal digital assistant), or a tablet, in additionto a normal server.

Note that by including the communication unit 122, the pulse measurementdevice 1 described here is configured so as to be capable of being usedover a network as well. However, the pulse measurement device 1 can alsobe configured as a standalone device by omitting the communication unit122.

The power source 113 is configured of a dry cell battery in thisexample, and supplies power to the various units in the pulsemeasurement device 1 in response to a user manipulating the power switchof the operating unit 115.

FIG. 3 illustrates an example of the circuit configuration of themeasurement unit 50 in the pulse measurement device 1. The measurementunit 50 includes a pulse driving circuit 47 that controls pulse drivingof the light-emitting element 54, an emitted light intensity controlcircuit 45 that controls the emitted light intensity (that is, a drivingcurrent) of the light-emitting element 54, a pulse wave signalamplifying circuit 46 that outputs a pulse wave signal S_(p) expressinga pulse by controlling a light-receiving sensitivity (that is, anamplifying gain of a photoelectric output) of the light-receivingelement 56, an A/D conversion circuit 44 that AD-converts the pulse wavesignal S_(P), an AC component amplifying circuit 40 that extracts an ACcomponent from the pulse wave signal S_(P), amplifies the AC component,and outputs the result as an AC component S_(AC), and an AC componentA/D conversion circuit 43. Note that the A/D conversion circuits 43 and44 may be provided within the CPU 111.

The CPU 111 functioning as the control unit is connected to the pulsedriving circuit 47, and the pulse driving circuit 47 controls a lightemission state (frequency and duty) of the light-emitting element 54 byswitching an NPN transistor based on a driving pulse supplied from theCPU 111. The CPU 111 is connected to the emitted light intensity controlcircuit 45, and the emitted light intensity control circuit 45 controlsthe emitted light intensity of the light-emitting element 54 by drivingthe light-emitting element 54 at a driving current defined by aresistance value of a variable resistance in accordance with an emittedlight intensity control signal from the CPU 111. That is, the emittedlight intensity (the amount of light emitted, in other words) of thelight-emitting element 54 increases as the driving current flowing inthe light-emitting element 54 increases.

The light-receiving element 56 outputs a photoelectric output inaccordance with the intensity of the received light. The pulse wavesignal amplifying circuit 46 amplifies the photoelectric output from thelight-receiving element 56 by increasing/reducing the resistance valueof the variable resistance in accordance with a photoelectric outputcontrol signal from the CPU 111, and outputs the result as the pulsewave signal S_(p). The signal outputted from the pulse wave signalamplifying circuit 46 is converted from an analog signal into a digitalsignal by the A/D conversion circuit 44. The digital pulse wave signalS_(p) is inputted into the CPU 111, and is used in a process forcalculating parameters and the like for controlling the emitted lightintensity.

FIG. 4 illustrates an example of the waveform of the pulse wave signalS_(p) outputted from the light-receiving element 56. Note that in FIG.4, the horizontal axis represents time (in seconds), and the verticalaxis represents the intensity of the pulse wave signal S_(P) (unit notshown). The pulse wave signal S_(P) is outputted as a waveform in whichan AC component (an alternating current component) S_(AC) thatfluctuates cyclically along with the pulsatory motion of a body (inother words, pulse waves in the blood) is superimposed on a DC component(a direct current component) V_(DC), that does not fluctuate cyclically,produced by light absorbed and scattered by tissue, accumulated blood,or the like. Note that normally, the magnitude (amplitude) of the ACcomponent S_(AC) is lower than the magnitude of the DC component V_(DC)by approximately two digits. Accordingly, it is desirable to extract theAC component S_(AC) from the pulse wave signal S_(P) and amplify theextracted signal so that the signal can be handled as data.

The AC component amplifying circuit 40 illustrated in FIG. 3 extractsthe AC component from the pulse wave signal S_(P) by carrying outbandwidth limitation using a band pass filter 41 that allows apredetermined frequency band (0.5 Hz-5 Hz, in this example) to pass onthe pulse wave signal S_(P) outputted from the pulse wave signalamplifying circuit 46, after which the AC component is amplified by anoperational amplifier (op-amp) 42 and is then outputted as the ACcomponent S_(AC). The op-amp 42 controls the amplifying gain of the ACcomponent by adjusting a resistivity between an input resistance and afeedback resistance (not shown) in accordance with an AC componentcontrol signal from the CPU 111. The AC component S_(AC) outputted fromthe op-amp 42 is converted into a digital signal AC component S_(AC) bythe AC component A/D conversion circuit 43. The digital AC componentS_(AC) is inputted into the CPU 111.

FIG. 5 illustrates an example of the waveform of the AC component S_(AC)inputted into the CPU 111. Note that in FIG. 5, the horizontal axisrepresents time (in seconds), and the vertical axis represents theintensity of the AC component S_(AC) (unit not shown). The AC componentS_(AC) changes cyclically at an amplitude V_(AC) in accordance with thepulsatory motion in the body (in other words, the pulse wave in theblood). The AC component S_(AC) is stored in the storage unit 112illustrated in FIG. 2, in time series.

Overall, the pulse measurement device 1 operates according to the flowof a pulse measurement method, illustrated in FIG. 9.

i) First, as indicated in step S11, functioning as a data obtainmentunit, the CPU 111 obtains the pulse wave signal S_(P) expressing thepulse by detecting the measurement subject's pulse using the measurementunit 50. The AC component amplifying circuit 40 extracts the ACcomponent from the pulse wave signal S_(P), amplifies the AC component,and outputs that component as the AC component S_(AC). The storage unit112 stores the AC component S_(AC) outputted by the AC componentamplifying circuit 40 in time series.

ii) Next, as indicated in step S12, functioning as a frequencyconversion unit, the CPU 111 converts the time-domain AC componentS_(AC) stored in the storage unit 112 into the frequency domain, andfinds a frequency spectrum of the AC component S_(AC).

In this example, a fast Fourier transform (FFT) is carried out for thefrequency conversion. At this time, as illustrated in FIG. 10, thetime-domain AC component S_(AC) stored in the storage unit 112 issegmented into periods having a predetermined length (four seconds, inthis example), and the frequency spectrum of the pulse wave signal S_(P)is found cyclically at timings t₁, t₂, t₃, and so on in each period.

Here, the frequency spectrum of the pulse wave signal S_(P) (the ACcomponent S_(AC)) is expressed as indicated by, for example, a solidline P illustrated in FIG. 6. Note that in FIG. 6, the horizontal axisrepresents a frequency (Hz), indicated at the top, or a pulse rate(BPM), indicated at the bottom, whereas the vertical axis represents theintensity of a frequency component of the pulse wave signal S_(P) (theunit normalized so that the maximum intensity peak is 100%; the sameapplies to FIGS. 7 and 8, mentioned later). In the example illustratedin FIG. 6, an intensity peak P₁ appears at approximately 30 BPM, anintensity peak P₂ appears at approximately 105 BPM, and an intensitypeak P₃ appears at approximately 210 BPM.

iii) Next, as indicated in step S13 of FIG. 9, functioning as a reststate determination unit, the CPU 111 determines whether or not themeasurement subject is at rest.

(a) Specifically, first, within a predetermined total frequency range(represented by W) that a person's pulse rate can take on, a frequencyrange in which the intensity of the frequency component of the frequencyspectrum exceeds a first threshold (represented by Th1) is found.

Here, finding a frequency range in which the intensity of the frequencycomponent of the frequency spectrum exceeds the first threshold Th1within the predetermined total frequency range W a person's pulse ratecan take on refers to focusing only on the main intensity peakscontained within the frequency spectrum and eliminating small intensitycomponents (in other words, frequency components produced bycomparatively light exercise performed by the measurement subject,harmonic components, and so on).

In this example, as illustrated in FIG. 6, the presupposed totalfrequency range W that a person's pulse rate can take on is set to arange from 30 BPM to 300 BPM.

In addition, in this example, the first threshold Th1 is set to 25%,which is a certain ratio with respect to the intensity of the maximumintensity peak among the intensity peaks P₁, P₂, P₃, and so on containedin the frequency spectrum (this is the intensity peak P₁ in the exampleillustrated in FIG. 6). In other words, when the intensity (raw data) ofthe maximum intensity peak P₁ contained in the frequency spectrum haschanged as a result of converting the time-domain pulse wave signalS_(P) into the frequency domain, in response to this, the firstthreshold Th1 is made variable and set to an appropriate value so thatlow-intensity components (for example, frequency components produced bycomparatively light exercise performed by the measurement subject,harmonic components, and the like; the intensity peak P₃ in the exampleillustrated in FIG. 6) are eliminated.

In the aforementioned example of FIG. 6, a frequency range W₁ from 30BPM to approximately 50 BPM corresponding to the intensity peak P₁ and afrequency range W₂ from approximately 75 BPM to approximately 120 BPMcorresponding to the intensity peak P₂ are found as frequency ranges,within the total frequency range (represented by W), in which theintensity of the frequency component of the frequency spectrum exceedsthe first threshold (represented by Th1).

(b) Next, it is determined whether or not the measurement subject is atrest based on whether or not a percentage (represented by OP) of thefrequency ranges W1,W2, and so on occupied within the total frequencyrange W is less than a second threshold (represented by Th2).

Here, in the case where the ratio of those frequency ranges (thefrequency ranges in which the intensity of the frequency component ofthe frequency spectrum exceeds the first threshold) with respect to thetotal frequency range W is less than a second threshold Th2, it isthought that only a basic intensity peak for when the measurementsubject is at rest is present in the total frequency range W, and thatother intensity peaks (different from the basic intensity peak) producedwhen the measurement subject exercises comparatively vigorously are notpresent. Accordingly, the rest state determination unit can correctlydetermine whether or not the measurement subject is at rest.

As in the aforementioned example in FIG. 6, in the case where there area plurality of frequency ranges in which the intensity of the frequencycomponent of the frequency spectrum exceeds the first threshold Th1 (W₁and W₂, in the example in FIG. 6) within the total frequency range W,those frequency ranges are totaled and the ratio percentage OP of thetotaled frequency ranges occupied within the total frequency range W iscalculated. In other words, the percentage OP is defined as:OP=(W ₁ +W ₂+ . . . )/W.

Meanwhile, in this example, the second threshold Th2 is set to 12.5%.

For example, in the example illustrated in FIG. 7 (when at rest), onlythe intensity peak P₁ exceeds the first threshold Th1 in the totalfrequency range W, and the frequency range W₁ in which the peak exceedsthe first threshold Th1 is a range from approximately 55 BPM toapproximately 65 BPM. In this case, the ratio OP of those frequencyranges with respect to the total frequency range W is:OP=W ₁ /W≈10 BPM/270 BPM<Th2Accordingly, in this example, it is determined that the measurementsubject is at rest.

On the other hand, in the example illustrated in FIG. 8 (duringexercise), the intensity peaks P₁, P₂, and P₃ exceed the first thresholdTh1 within the total frequency range W, and the respective frequencyranges W₁, W₂, and W₃ in which those respective peaks exceed the firstthreshold Th1 are ranges of approximately 70 BPM to approximately 90BPM, approximately 130 BPM to approximately 140 BPM, and approximately160 BPM to approximately 170 BPM. In this case, the ratio OP of thosefrequency ranges with respect to the total frequency range W is:OP=(W ₁ +W ₂ +W ₃)/W≈40 BPM/270 BPM>Th2Accordingly, in this example, it is determined that the measurementsubject is exercising.

In this manner, it is determined whether or not the measurement subjectis at rest.

iv) Then, as indicated in step S14 of FIG. 9, functioning as a pulserate obtainment unit, the CPU 111 finds the pulse rate from the point intime when the measurement subject has been determined to be at rest asthe measurement subject's at-rest pulse rate.

In this example, the CPU 111 finds, as the measurement subject's at-restpulse rate, a frequency indicating the maximum intensity peak from amongthe intensity peaks contained in the frequency spectrum.

For example, in the example illustrated in FIG. 7 (when at rest), afrequency of 60 Hz, indicated by the maximum intensity peak P₁, is foundas the measurement subject's at-rest pulse rate.

Through this, using the aforementioned frequency conversion result, themeasurement subject's at-rest pulse rate can be found with ease.

As a result, according to the pulse measurement device 1, themeasurement subject's at-rest pulse rate can be measured correctly.

v) After this, as indicated in step S15 of FIG. 9, the CPU 111 tracksand finds the measurement subject's pulse rate during exercise, usingthe at-rest pulse rate as a reference.

Through this, the measurement subject's pulse rate during exercise canbe correctly measured.

In the above example, in step S13 of FIG. 9, as illustrated in FIG. 10,the frequency spectrum of the pulse wave signal S_(P) (the AC componentS_(AC)) is found cyclically every period of a given length (fourseconds, in this example), and whether or not the measurement subject isat rest is determined for each frequency spectrum, or in other words,for each period. However, the invention is not limited thereto. It maybe determined whether or not the respective ratios OP for each frequencyspectrum are less than the second threshold Th2, and the measurementsubject may be determined to be at rest when the ratio OP is less thanthe second threshold Th2 multiple times (for example, two times, namelythe timing t₁ and t₂) in sequence. Through this, whether or not themeasurement subject is at rest can be determined even more correctly.

Alternatively, as illustrated in FIG. 11, AC component data from aperiod of a given length (16 seconds, in this example) may be obtainedfrom the storage unit 112 cyclically in five-second cycle timings t₁,t₂, t₃, . . . and undergo frequency conversion, and it may then bedetermined whether or not the ratio OP for each frequency spectrum isless than the second threshold Th2 with each obtained frequencyspectrum, or in other words, with each period, after which it may bedetermined whether or not the measurement subject is at rest. In thiscase, the target period for frequency conversion becomes longer, andthus whether or not the measurement subject is at rest can be determinedeven more correctly. In addition, even in the case where the frequencyconversion is carried out at the timing illustrated in FIG. 11, themeasurement subject may be determined to be at rest when the ratio OP isless than the second threshold Th2 multiple times (for example, twotimes, namely the timing t₁ and t₂) in sequence, in the same manner.Through this, whether or not the measurement subject is at rest can bedetermined even more correctly.

In addition, in the aforementioned example, when it is determined instep S13 of FIG. 9 that the measurement subject is at rest, in step S14of FIG. 9, a frequency indicating the maximum intensity peak containedin the frequency spectrum that serves as the evidence for thatdetermination is found as the measurement subject's at-rest pulse rate.However, the invention is not limited thereto. The number of peaks orvalleys in the AC component S_(AC) of the pulse wave signal S_(P) may becounted, and the measurement subject's at-rest pulse rate may be foundbased on the number of repetitions in the AC component S_(AC) (the BPM).

The aforementioned pulse measurement method may be constructed as aprogram for causing a computer to execute the method.

Such a program (a pulse measurement program) may be recorded on acomputer-readable recording medium such as a CD-ROM or the like, andmade distributable in such a form. By installing the pulse measurementprogram in a generic computer, the aforementioned pulse measurementmethod can be executed by the generic computer.

In addition, a program stored in the storage unit 112 may be encoded ona memory or other non-transitory computer-readable recording medium (amemory, a hard disk drive, an optical disk, or the like), and a genericcomputer may then be caused to execute the aforementioned pulsemeasurement method.

Although the CPU 111 carries out a fast Fourier transform (FFT) as thefrequency conversion in the aforementioned example, the invention is notlimited thereto. Any other conversion method may be employed as long asthe method is capable of converting the time-domain pulse wave signalS_(P) into the frequency domain.

The aforementioned embodiments are merely examples, and many variationsthereon can be carried out without departing from the scope of thisinvention.

REFERENCE SIGNS LIST

-   -   10 main body    -   50 measurement unit    -   54 light-emitting element    -   56 light-receiving element    -   111 CPU

What is claimed:
 1. A pulse measurement device comprising: a pulse wavesensor configured to be attached to a measurement subject and to detectpulses of the measurement subject and generate pulse wave signals; astorage configured to store the pulse wave signal; and a controllerconfigured to function as: a data obtainment unit to obtain a pulse wavesignal expressing a pulse by detecting a pulse of the measurementsubject using the pulse wave sensor; a frequency conversion unit toconvert the pulse wave signal in a time-domain stored in the storage toa frequency spectrum in a frequency domain, and to find one or morefrequency ranges in which the intensity of the frequency spectrumexceeds a first threshold, the frequency spectrum having variableintensity with respect to frequency change and covering at least apredetermined total frequency range W, the predetermined total frequencyrange W covering possible pulse rates of a person; and a rest statedetermination unit to determine whether or not a percentage of the oneor more frequency ranges occupied within the predetermined totalfrequency range W is less than a second threshold; to determine that themeasurement subject is at rest when (i) an exceeding frequency rangewithin the predetermined total frequency range W is found, and when (ii)a ratio of a width of the exceeding frequency range with respect to awidth of the total frequency range W is found to be less than the secondthreshold; and to determine the measurement subject's at-rest pulse ratewhen the measurement subject is determined to be at rest.
 2. The pulsemeasurement device according to claim 1, wherein the pulse wave sensoris a photoelectric sensor including a light-emitter configured to emitlight toward a measurement area at a given emitted light intensity and alight-receiver that receives light reflected by or transmitted throughthe measurement area.
 3. The pulse measurement device according to claim2, wherein the first threshold is set to a ratio with respect to anintensity of a maximum intensity peak among intensity peaks contained inthe frequency spectrum.
 4. The pulse measurement device according toclaim 1, wherein the first threshold is set to a ratio with respect toan intensity of a maximum intensity peak among intensity peaks containedin the frequency spectrum.
 5. The pulse measurement device according toclaim 1, wherein the frequency conversion unit segments the pulse wavesignal in the time-domain stored in the storage into periods of apredetermined given length and finds the frequency spectrum of the pulsewave signal by converting the pulse wave signal into the frequencydomain cyclically; and the rest state determination unit determineswhether or not the ratio is less than the second threshold for thefrequency spectra of the pulse wave signal found cyclically, anddetermines that the measurement subject is at rest when the ratio isless than the second threshold a plurality of times in succession. 6.The pulse measurement device according to claim 1, wherein thecontroller is further configured to track and find the measurementsubject's pulse rate during exercise, using the at-rest pulse rate as areference.
 7. A pulse measurement method comprising: detecting pulseswith a pulse wave sensor configured to be attached to a measurementsubject and to detect pulses of the measurement subject and generatepulse wave signals; obtaining a pulse wave signal expressing a pulse bydetecting a pulse of the measurement subject using the pulse wave sensorand storing the pulse wave signal in a storage; converting the pulsewave signal in a time-domain stored in the storage to a frequencyspectrum in a frequency domain, the frequency spectrum having variableintensity with respect to frequency change and covering at least apredetermined total frequency range W, the predetermined total frequencyrange W covering possible pulse rates of a person; finding one or morefrequency ranges in which the intensity of the frequency spectrumexceeds a first threshold; determining whether or not a percentage ofthe one or more frequency ranges occupied within the predetermined totalfrequency range W is less than a second threshold; determining that themeasurement subject is at rest when (i) an exceeding frequency rangewithin the predetermined total frequency range W is found, and when (ii)a ratio of width of the exceeding frequency range with respect to awidth of the total frequency range W is found to be less than the secondthreshold; and determining the measurement subject's at-rest pulse ratewhen the measurement subject is determined to be at rest.
 8. The pulsemeasurement method according to claim 7, further comprising: trackingand finding the measurement subject's pulse rate during exercise, usingthe at-rest pulse rate as a reference.
 9. A computer-readablenon-transitory medium storing a program for causing a computer toexecute the pulse measurement method according to claim
 7. 10. A devicefor determining a rest state comprising: a pulse wave sensor configuredto be attached to a measurement subject and to detect pulses of themeasurement subject and generate pulse wave signals; a storage; aprocessor, and a non-transitory computer-usable medium having computerreadable instructions stored on the processor that, when executed by theprocessor, causes the processor to perform operations for controllingthe device, the operations comprising: obtaining a pulse wave signalexpressing a pulse by detecting a pulse of the measurement subject usingthe pulse wave sensor; storing the pulse wave signal in the storage;converting the pulse wave signal in a time-domain stored in the storageto a frequency spectrum in a frequency domain, the frequency spectrumhaving variable intensity with respect to frequency change and coveringat least a predetermined total frequency range W, the predeterminedtotal frequency range W covering possible pulse rates of a person;finding one or more frequency ranges in which the intensity of thefrequency spectrum exceeds a first threshold; determining whether or nota percentage of the one or more frequency ranges occupied within thepredetermined total frequency range W is less than a second threshold;determining that the measurement subject is at rest when (i) anexceeding frequency range within the predetermined total frequency rangeW is found, and when (ii) a ratio of a width of the exceeding frequencyrange with respect to a width of the total frequency range W is found tobe less than the second threshold; and determining the measurementsubject's at-rest pulse rate when the measurement subject is determinedto be at rest.
 11. The device according to claim 10, the operationsfurther comprising: tracking and finding the measurement subject's pulserate during exercise, using the at-rest pulse rate as a reference.